A worker with the Municipal Corporation of Delhi sprays insecticide in New Delhi, November 2006.

There’s a lot of news aroundof a higher-than-normal outbreak of dengue in New Delhi. But signs are that it’s the south of the country where the spread of dengue is more worrisome.

Health experts say there’s no evidence so far the incidence of the disease this season is above average in the capital. Every year the media makes too much of the uptick in cases of dengue in October, said N.K. Yadav, a health officer with the South Delhi Municipal Corporation.

Most cases in a year happen in October as that’s just after the monsoon rains during which the mosquitoes that carry the dengue virus proliferate. “This is nothing unusual,” Mr. Yadav said.

Manish Kakkar, a senior public health specialist at the Public Health Foundation of India, a New Delhi-based independent body, also says it’s too early to draw any conclusions from the recent reports.

So far this year, there have been 330 cases of dengue and one confirmed death, including 150 in the past week, in line with last year’s figures up to this point, according to New Delhi official statistics. In 2011 in total, there were 1,131 cases and eight deaths.

For now, the government appears to be more concerned about the south of the country. On Friday, Health Minister Ghulam Nabi Azad held a meeting in Chennai to push southern states to be more aggressive in prevention of dengue after an uptick in cases.

The government, in a statement, said the five southern states had reported a total 12,500 cases through September this year, about four times the number in the same period of 2011. The disease has caused 77 deaths versus 33 last year.

(Statistics on dengue are notoriously hard to get, health experts say. Here’s a list of official statistics on dengue from across India since 2007, in which numbers for the southern states and Delhi differ from those cited above.)

Global dengue infections have increased rapidly in recent years. The U.N.’s World Health Organization estimates there are 50 million to 100 million cases annually and 40% of the world’s population is at risk of getting the disease.

The virus is transmitted between humans by the Aedes aegypti mosquito and is common in tropical and sub-tropical climates. In more recent years the disease has become more common and even recorded in colder climates like Bhutan.

The illness causes flu-like symptoms but rarely results in death. Severe cases, involving persistent vomiting and abdominal pain, may require intravenous rehydration to ensure adequate levels of body fluid. See this from the WHO for more details.

Unlike other mosquitoes, the Aedes aegypti is a daytime feeder, meaning it’s important not to become exposed at peak biting times in the early morning and just before dusk. Authorities also can fog danger-prone areas. There is no vaccine against dengue.

The best way to guard against the disease is to make sure there are no containers where rain water can collect, experts say. The Aedes aegypti proliferates in urban habitats in water collected in man-made containers.

Some countries have had success in stamping out dengue through penalizing residents who allow water to stand. Singapore is seen as the poster boy for this approach, handing out hefty fines and banning roof drains on new buildings as they are hard to clean. The result was a sharp drop in dengue cases.

India also has imposed fines on residents, but the penalties have been as low as 500 rupees ($10) and enforcement spotty. One of the main hypotheses for a dengue epidemic in Delhi in 2010 – when there were 6,259 cases and eight deaths – was because of municipal construction for the Commonwealth Games that year. Building sites for new roads, stadiums and other infrastructure led to water pooling and more breeding grounds for mosquitoes during an exceptionally heavy monsoon.

Mr. Kakkar, the public health expert, says south Delhi has seen above-average numbers of dengue cases in recent years. This could be due to the fact that many colonies in the area don’t have piped water, meaning residents have to use storage tanks, he said. Failure to enclose these containers offers a breeding ground.

Another reason South Delhi is hit, Mr. Kakkar added, could be that wealthier residents in these neighborhoods are unwilling to allow public health officials into their houses to evaluate whether they are following best practices. A water tank needs to be enclosed or cleaned every week in the peak season to ensure new mosquitoes don’t breed.

While Delhi authorities often get criticized, communities have to take responsibility, Mr. Kakkar said. “There has to be a cultural shift.”

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